Conventionally, in addition to main grooves that extend in a circumferential direction of a tire and sub-grooves that extend in a width direction of the tire, all-season pneumatic tires that are used throughout the year also have sipes on a tread surface in order to demonstrate favorable snow performance. An example of this type of pneumatic tire is the commonly known tire shown in FIG. 8.
This pneumatic tire has four main grooves 42 that extend in the circumferential direction of the tire formed in a tread surface 41. Additionally, five land portions 43 are formed by these four main grooves 42. Each of the land portions 43 has sub-grooves 44 and sipes 45 that extend in the width direction of the tire, and the center land portion 43A located between the inside main grooves 42 is formed into ribs 43A1 and blocks 43A2. Center land portion 43B located between inside main grooves 42 and outside main grooves 42, and shoulder land portions 43C located to an outer side in the tire width direction of the outside main groove 42 are respectively formed into blocks (refer to Japanese Patent Publication (A) No. 2007-230251).
Incidentally, in recent years there has been demand for increased safety with respect to pneumatic tires in conjunction with higher vehicle performance. The aforementioned all-season pneumatic tires are no exception, and additional improvements are desired.